Local News

Greenhead flies are back with a vengeance. Here’s what to know.

Greenheads, AKA horseflies, are on beach patrol in Essex County.

A greenhead fly on the leg of an unfortunate victim. Keith Bedford

July 12, 2025

1 minute to read

Greenhead season is in full swing as the green-eyed horsefly with a notoriously nasty bite descends on Massachusetts beaches.

Greenhead flies typically emerge from eggs inside salt marshes at the end of June, which is prime time for beachgoers. According to a WBUR report, the pesky pests are a particular problem on North Shore beaches in the Great Marsh area.

Barry Noon, the director of the Northeastern Massachusetts Mosquito Control and Wetlands Management District (MCWM), told the outlet that his team sets 485 greenhead traps across Essex County every season, but that it’s impossible to capture all of them.

However, Noon estimated that the traps catch between 5,000 and 8,000 horseflies each year. The goal is to bring the greenhead population to a manageable level so people can enjoy the beach.

But for those unfortunate enough to have their sunbath interrupted by a greenhead bite, one fly is too many.

“Because they occur in great numbers, the females bite during daylight, they can fly for miles, attack persistently domestic animals and people, and they interfere with the enjoyment of coastal areas throughout much of the summer,” MCWM officials said on the department’s website.

While the bites are painful and may cause allergic reactions, experts say the flies don’t transmit disease.

People can minimize the likelihood of getting bitten by wearing lighter clothes and towels, drying off after swimming, and wearing long-sleeved shirts. MCWM experts caution that sprays, perfumes, and “increased metabolic activity” attract the biting flies.

The greenhead season is due to die down in September.